Apparatus for sensing the unstressed shape of a thin strip subjected to high tensile stress

ABSTRACT

A cold rolling mill is described wherein the unstressed shape of metal sheet is continuously sensed during rolling by a plurality of negligible displacement force sensors perpendicularly disposed relative to the pass line at a mill location producing a tensile stress above 4,000 p.s.i. in the metal sheet being rolled. The output signals from those sensors underlying opposite edges of the metal sheet are compared to equalize reduction at the sheet edges while the difference between the force measured by a centrally situated sensor and the average force measured by the sensors underlying opposite edges of the sheet provide a signal indicative of the roll bending force required to produce flat sheet.

D United States Patent 1 1 3,581,536

[72] Inventor Geo g E- rw g r 2,809,519 10/1957 Kaestner 73/159 Schenectady,N.Y. 2,903,926 9/1959 Reichl l. 72/8 [21] Appl No. 835,844 3,081,651 3/1963 Roberts 72/9 [221 Filed Apr. 17, 1969 3,213,655 10/1965 Reid 72/11 Division of Ser. No. 750,676, July 8, 1968, 3,334,508 8/1967 Martin l. 72/9X abandoned, Continuation of Ser. No. 3,431,761 3/1969 Clement .l 72/1 1 P 506,984, Nov. 9, 1965, abandoned. 3,442,104 5/1969 Misaka et l 1 72/9 [45] atented June 1, 1971 Pnma Examiner-Milton S. Mehr 73 Assignee General Electric Company Anomey oscar B. wadde [54] APPARATUS FOR SENSING THE UNSTRESSED SHAPE OF A THIN STRIP SUBJECTED TO HIGH TENSILE STRESS 3 Claims, 5 Drawing Figs.

[52] US. Cl .1 72/9, 72/17, 72/34 [51] Int. Cl B2lb 37/06 [50] Field of Search 72/8, 9, 10, 1 1, l6, 17, 34

[56] References Cited UNITED STATES PATENTS 2,674,127 4/1954 Garrett et al. 73/159 ABSTRACT: A cold rolling mill is described wherein the unstressed shape of metal sheet is continuously sensed during rolling by a plurality of negligible displacement force sensors perpendicularly disposed relative to the pass line at a mill location producing a tensile stress above 4,000 p.s.i. in the metal sheet being rolled. The output signals from those sensors underlying opposite edges of the metal sheet are compared to equalize reduction at the sheet edges while the difference between the force measured by a centrally situated sensor and the average force measured by the sensors underlying opposite edges of the sheet provide a signal indicative of the roll bending force required to produce flat sheet.

PAIENIEDJUN nan 3,581,536

' Sam 1 or 2 Q48 \Y a 5o INVENTOR. Q 7 54 GEORGE LTERWILLIGER HIS ATTORNEY APPARATUS FOR SENSING THE UNSTRESSED SHAPE OF A THIN STRIP SUBJECTED TO HIGH TENSILE STRESS This application is a divisional application of copending application, Ser. No. 750,676, filed July 8, 1968 (now abandoned), the latter application being a continuation application of now abandoned application, Ser. No. 506,984, filed Nov. 9, I965.

The present invention pertains to means for providing an anticipatory indication of the unstressed shape of a thin strip when the strip shape is distorted by an externally applied tensile force. The invention is particularly useful for predicting the shape of a thin metal strip progressing through the stands of a cold rolling mill and, accordingly, will be described in this environment.

The shape of a thin metal strip, or sheet metal body, as used herein refers to properties that determine whether the strip will lie flat when supported on a planar surface in the absence of forces applied to the strip in the principal plans thereof, or whether the strip will exhibit central buckles, curls, and/or wavy edges under these conditions. Thus, variations in thickness of the strip along are not of significance. In most sheet metal applications wide thickness tolerances exist whereas the least amount of buckle, for example, results in an unmarketable product.

In most cold rolling mill installations, shape control is a major problem. Flat shape for the end product cannot be insured by adjusting the mill rolls to provide uniform transverse thickness. This is because the strip to be rolled oftentimes comes to the mill with nonuniform transverse thickness. For example, the strip has commonly previously been worked upon by a hot rolling mill wherein a crown is ordinarily intentionally provided to aid tracking through such rolling mills. In passing, it will be noted that the shape problem is not as severe in hot rolled material because of the tendency of the heated metal to flow and relax internal stresses.

Various systems have been devised to bend work rolls and vary the applied pressure transverse of the strip being rolled. One such system is described in US. Pat. No. 3,024,679 by T. A. Fox. With systems of this kind an operator observes the shape of the finished product and makes away any necessary corrections in the various adjustments of the mill work rolls. The operator must observe the finished product because the strip is normally subjected to a great tensile stress in the rolling mill which causes the strip to appear flat, regardless of its actual ultimate shape. It would be highly desirable to provide means for giving an anticipatory indication of the unstressed shape of the rolled strip so that an operator could more accu rately and quickly adjust the work rolls to provide a flatshaped product. Alternatively, the sensing means should advantageously be readily adapted to enable automatic control of strip shape.

Accordingly, it is an object of my invention to provide means for sensing the unstressed shape of a thin strip subjected to tensile forces.

It is another object of my invention to provide an indication of the ultimate shape ofa metal strip passing through a rolling mill.

Briefly, l have discovered that the relative magnitudes of forces exerted on a plurality of force sensing means disposed transversely ofa strip in tension provide a reliable anticipatory indication of the unstressed strip shape. Thus, I provide at least one force sensing means disposed near the center of the strip and at least one other force sensing means disposed near an edge of the strip. Preferably, the force sensing means include rollers biased against a major surface of the strip. I have found that adjustment of the mill work rolls to maintain the sensed forces as nearly equal as possible results in optimum flat shape for the rolled product. On the other hand, the extent of departure from equality of these forces provides a reliable indication of the extent of buckle or edge wave produced.

The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. My invention, however, both as to organization and method of operation, together with further objects and advantages thereof, may be best un derstood by reference to the following description taken in connection with the accompanying, drawings wherein corresponding components are similarly designated and in which:

FIG. 1 illustrates a shape indicator in accord with one embodiment of the invention;

FIG. 2 is a side view of one of the force sensing elements of FIG. I;

FIG. 3 is a view similar to FIG. 2 showing an alternative kind of force sensing element suitable for use in accord with the invention;

FIG. 4 illustrates schematically an alternative display suitable for the shape indicator ofthe invention; and,

FIG. 5 is a schematic diagram of a system for providing automatic correction signals responsive to the output of the shape indicator.

The shape indicator of FIG. I includes a plurality of force sensors l7 each having a corresponding frame 8-44 carrying respective rollers I52I journaled therein and adapted to bear against the underside of a rolled strip 22. Sensors I7 are preferably disposed in a row transverse to strip 22; i.e., the sensors are disposed perpendicularly to the pass line of the rolling mill. The edges of rollers l52l are advantageously rounded, as at 23 and 24 on roller 15, in order to prevent catching the edge of strip 22, particularly when strips of nar rower width are to be accommodated.

A plurality of display devices 25-3l are provided for sensors l7, respectively, and are positioned to provide an indication of the relative forces exertedl on the various sensors through rollers l5-2I. Sensors I-7 are conveniently selected to be of the electromechanical transducer kind, in which case display devices 25-31 can be electrical voltmeters with linear scales and electrically connected to the output of sensors l-7, respectively, by means ofa wiring harness 32. In this case, cable 33 of harness 32 is coupled to sensor 1 and remaining cables 3439 of harness 32 are coupled to sensors 2-7, respectively.

A suitable mechanical structure for sensors l-7 is more clearly set forth in the side view of FIG. 2 wherein the portion of strip 22 shown has passed through work tools 40 and 41 of one stand of the rolling mill and is urged upwardly by roller 15 that bears against the underside of strip 22. Frame 8 is pivotally journaled at 42 in a rigid support member 43 which is, in turn, secured to a stable platform 44, as by bolts 45, for example.

Roller 15 is journaled in frame 8 by antifriction bearings, that can be ball bearings as illustrated at 46, which rotatably support the axle 47 of roller I5. Force sensor 1 abuts platform 44 and frame 8, and urges roller 15 upwardly against strip 22 with a magnitude of force which is conveniently adjustable by means of a threaded lock bolt 48, or the like, that serves as a biasing means. It will be understood: that strip 22 proceeds subsequently to another set of work rolls or a takeup reel (not shown) and is under a high tensile stress. Thus, strip 22 may be considered to be tightly stretched over the rollers, as roller 15. Of course, a suitable alternative in many cases involves urging the indicator downward against the topside of strip 22, in which case the relationship of components can be visualized by holding FIG. 2 upside down.

There are many known force sensors suitable for use in the present invention. In general, it is preferred that the sensor be of the negligible displacement kind in order to provide the most accurate indications of shape. Such sensors commonly employ resistance strain gauges or strain sensitive semiconductive materials. Accordingly, display devices 25-3l will ordinarily include a series-conducted source of electric potential, that can be a battery, in which event the display elements serve as the usual ohm-meter. All that is required is that the display respond to the forces exerted by strip 22 on rollers 15- 21 to provide an indication of the relative magnitudes of the forces. By way of specific example, force sensing means suitable for use in this invention are disclosed in US. Pat. No. 2,472,047, Ruge.

In operation, the various force sensors, or display devices, are adjusted to provide predetermined relative responses when the rolled strip has a flat unstressed shape. Preferably, the responses are selected to be substantially equal under the aforementioned condition. Thereafter, one or more sets of work rolls are adjusted in crown height or differential end force as required to maintain the selected predetermined relative responses. One suitable means for adjusting work roll crown is disclosed in the aforementioned US. Pat. No. 3,024,679, Fox and features bending the work rolls by exerting a controllable force between the journals of the work rolls and backup rolls. Alternatively, the force can be exerted directly between the work rolljournals, as by a hydraulicjack.

When the relative indicated force on the central sensors increases relative to the indicated force on the end sensors, it signifies that the total roll force is too great for the roll crown. This 'can be corrected in one or more of the following ways: (1) decreases the total roll force to decrease the draft, or percentage reduction, in the stand; (2) increase the tension level in the strip between stands; (3) increase the external force between the work roll bearings; (4) decrease the external force between the backup and work rolls; or (5) substitute work rolls with a higher crown. It is apparent that l through (4) are readily adapted to automatic control. When the relative indicated force on the central force sensors decreases, then correction is obtained by reversing one or more of the foregoing enumerated procedures. Similarly, a rise in indicated force at either end of the shape indicator relative to the to the end shows the need for increasing the force at that end of the work rolls. The indicated corrective action can be accomplished manually or by automatic means. Differential end force on the rolls is conveniently adjusted by operating the mill screwdowns independently.

The alternative force sensor assembly of FIG. 3 features a beam 50 adjustably cantilevered in a support 5] at one end and carrying a joumaled roller 52 at the other end. A pair of resistance strain gauges 53 and 54 sense the bending stress in beam 50. The bending stress is, of course, proportional to the reaction force exerted on roller 52 by strip 22, over a wide range. Two resistance gauges are employed as shown in the preferred embodiment to permit any of the well'known bridge connections to be used wherein undesired extraneous effects are cancelled and sensitivity of measurement increased by a factor of two.

FIG. 4 illustrates schematically a display that features an oscilloscope 59 as a suitable alternative to display devices 25- 31 of FIG. 1. The system features two rotatable potentiometers 60 and 61 driven together, as by a common shaft connected to motor 62. The horizontal sweep is generated by rotation of wiper arm 63 around the stator 64 of potentiome ter 61. Opposite extremities of stator 64 are connected to a suitable source of electric potential, that can be a battery as shown schematically at 65. The midpoint 66 of stator 64 is grounded to provide a symmetrical horizontal sweep across the face of oscilloscope 59.

The vertical input signal, indicative of the unstressed shape of the rolled strip, is generated as wiper 67 rotates around stator 68 of potentiometer 60. Cables 33 through 39, as discussed in conjunction with FIG. 1, are connected at equidistant respective circumferential taps about stator 68. Wiper arm 67 is connected to vertical input terminal of oscilloscope 59 and to a suitable power supply, illustrated schematically as battery 69 having the negative terminal grounded and the positive terminal connected to wiper arm 67 through a series resistance 70. Thus, changes in resistance of the sensors connected to respective cables 33-39, in response to variations in sensed force, provide corresponding changes in the voltage at the vertical terminal of oscilloscope 59, as will be readily understood by those skilled in the art. In this way, variations in the height of oscilloscope trace can be used to monitor the relative forces exerted upon the various sensors, and necessary corrective action can be taken to insure flat strip shape, as previously described.

FIG. 5 is a simplified schematic circuit diagram of a suitable means for providing electric control signals that change in magnitude in response to variations in the relative forces exerted on the force sensing means. Two electric control signals are provided. The first signal is responsive in magnitude and polarity to difference in force at the ends of the rolled strip and the second signal is responsive in magnitude an polarity to the difference in force at the center of the rolled strip as compared to the average value of force at the ends of the strip. It will be recalled that the former is useful in providing a correction to the backup rolls to equalize rolling at the edges of the work rolls, whereas the latter is useful in providing a corrective bending force to the work rolls, for example, all in the interest of rolling a strip of flat shape.

Cables 33-39 correspond to the similarly designated components of FIG. 1 and the force sensing means are represented by respective dashed resistances 73-79. While the force sensing means are depicted as variable resistance elements for purpose of this illustration, other kinds can be used equally well in most cases, including the readily adaptable variable voltage devices. As illustrated in FIG. 5, cables 33 and 34 are connected to each other and to a suitable power supply comprising a battery and an adjustable resistance 8] by means of conductor 82. Cables 38 and 39 are similarly connected together and to battery 83 and an adjustable resistance 84 by means of conductor 85. Suitable output means for this first portion of the circuit take the form of terminals 86 and 87 that are connected respectively to the junction of battery 80 and resistance 81 and the junction of battery 83 and resistance 84. A zero-center voltmeter 88 is conveniently connected across terminals 86 and 87 to monitor the difference in potential of these terminals.

In operation of the circuit thus far described, resistance 81 and 84 are preferably adjusted to center voltmeter 88 when the relative forces at the edges of the strip are as desired to provide a flat shape product. Thereafter, the electric control signal from output terminals 86 and 87 will respond to departures in the relative magnitudes of the forces to provide a corresponding deflection of the needle of voltmeter 88. While the control signal, in the illustrative embodiment, responds both in polarity and magnitude to changes in the relative magnitudes of the edge forces, departures in magnitude only about a steady state value will serve equally well in most cases. It should be noted that the electric control signal is responsive only to changes in the relative magnitudes of the forces sensed and not to uniform variations in the absolute magnitude of the forces. The latter variations cancel in the circuit described.

Of particular significance is provision of an electric control signal responsive to difference in the magnitude of sensed forces near the edges of the rolled strip and the magnitude of sensed forces near the center of the rolled strip. Toward this end, cables 35, 36 and 37 are connected together and, by means of conductor 90, connected to a suitable power supply shown schematically as including battery 91 and adjustable resistance 92. Thus, the output voltage at terminal 93, that is connected to the junction of battery 91 and resistance 92, corresponds in magnitude to the force sensed near the center of the rolled strip. A voltage of like magnitude and polarity responsive to the edge forces is provided at terminal 94, that is connected to the junction 95 of a resistance divider network connected across output terminals 86 and 87 and comprising resistances 96 and 97. Voltmeter 98 is connected across terminals 93 and 94 to provide a convenient monitor of the elec tric control signal which is responsive to the difference in magnitude between the sensed forces at the central portion of the strip and the sensed forces near the edges of the strip. In the interest of more completely balancing changes in absolute magnitude of the aforementioned forces, an additional force sensing resistance element can be provided for one of the central force sensing means or an additional central force sensing means can be provided although this is ordinarily not required in view of the small range of force deviations normally encountered in practice.

By way of more clearly setting forth the invention and in the interest of not embarking upon a complicated discussion of circuits that may tend to detract from the central theme, the illustration of HO. 5 has been confined to passive circuit elements. It will occur to those skilled in the art, however, that active devices as vacuum tubes, transistors and the like can oftentimes by advantageously used for buffer amplifiers, for example, and that many ofthe well-known measuring bridge net works, as the Wheatstone bridge, can be employed. ln addition, the control signals can in most instances be strengthened and isolated by means of the customary difference amplifiers. The foregoing techniques are also useful in minimizing current flow through or from the force sensing elements, to name but one additional advantage.

It is apparent that in the most basic application of the present invention wherein only work roll bending need by controlled, all that is required is one force sensing means posi tioned approximately at the center pass line of the rolling mill and the other force sensing means near the edge of the mill. In the next increment toward precision control, three force sensing means would be used and so on until the degree of precision economically justifiable in the particular situation is achieved. In automated cold rolling mills it is particularly advantageous to utilize many force sensing means in accord with this invention to provide separate inputs to a computer that not only controls necessary corrective action but also preserves a permanent record of the shape profile of the product produced' In this way the rolled strips can be allocated to end uses tailored to accommodate a particular small amount of buckle, curl or wavy edge formed in a given production run, rather than scrapping the product.

As for the particular preferred position of the shape indica tor relative to the stands of the rolling mill, l have found that it is definitely desirable that the average longitudinal tensile stress (in the direction ofthe mill pass line) in the strip should exceed 4,000 psi. for optimum results. Accuracy of anticipated shape indication drops sharply for strip tension less than this minimum value. Accordingly, in mills wherein the takeup reel at the finish end ofthe mill provides a lesser tensile stress, the shape indicator is advantageously positioned in one of the spans between work rolls where much higher tensile stress is normally present. Otherwise, the exact position is not critical, although in the interest of most closely anticipating shape of the end product, I prefer to position the indicator as close to the finish end of the rolling mill as is consistent with the aforementioned criterion of insuring more than 4,000 psi. tensile stress in the strip.

When making the preliminary adjustments of the shape sen sor, it is convenient to provide a substantially flat-shaped test strip in the rolling mill under the expected normal amount of tension. Resistance strain gauges are thereafter positioned on the opposite side of the strip over each of the force sensing means. The force sensing means are thereafter adjusted to provide an indication corresponding to the measured value of stain and the electrical circuit is balanced. Then the test strip is removed and the calibrated shape sensor is ready for operation.

According to the provisions ofthe patent statures, l have explained the principles of my invention and have illustrated and described what I now consider to represent its best embodiments. However, l desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A cold rolling mill for cold rolling a strip of steel comprising a plurality of rolling stands each characterized by a pair of work rolls, a plurality of substantially negligible displacement force sensing means disposed at spaced-apart locations substantially transversely of the mill pass line said means being situated within said mill at a downstream location whercat the average longitudinal tensile stress within said strip is above 4,000 p.s.i., means for biasing said force sensing means against a principal surface of said strip as the strip passes through the mill, at least one force sensing means or sensing reaction force of the strip being disposed adjacent each edge of said strip, electrical means responsive to the difference between the relative magnitude of forces sensed at the strip edges to provide a signal proportional in magnitude and polarity to the difference in force at the ends of the rolled strip, a separately activated screwdown at each end of at least one of said work rolls immediately upstream of said force sensing means, and means responsive to said difference signal for activating one screwdown to screwdown one end of one of said work rolls.

2. A cold rolling mill for cold rolling a strip of steel as claimed in claim l wherein said force sensing means are strain sensitive transducers and further including at least one force sensing means disposed centrally of the strip, electrical means responsive to said center force sensing means and said edge sensing means for producing a signal proportional in magnitude and polarity to the difference in force at the center of the rolled strip as compared to the average value of the forces measured simultaneously at the ends of the strip, and means responsive to the signal indicating the difference between the force at the center of the rolled strip compared to the average value of the forces at the ends of the strip for bending said work rolls to adjust the work roll crown by an amount proportional to said difference between forces.

3. A cold rolling mill for cold rolling a strip of steel according to claim 1 wherein said force sensing means are positioned between stands of the rolling mill. 

2. A cold rolling mill for cold rolling a strip of steel as claimed in claim 1 wherein said force sensing means are strain sensitive transducers and further including at least one force sensing means disposed centrally of the strip, electrical means responsive to said center force sensing means and said edge sensing means for producing a signal proportional in magnitude and poLarity to the difference in force at the center of the rolled strip as compared to the average value of the forces measured simultaneously at the ends of the strip, and means responsive to the signal indicating the difference between the force at the center of the rolled strip compared to the average value of the forces at the ends of the strip for bending said work rolls to adjust the work roll crown by an amount proportional to said difference between forces.
 3. A cold rolling mill for cold rolling a strip of steel according to claim 1 wherein said force sensing means are positioned between stands of the rolling mill. 